Non-aqueous electrolyte battery

ABSTRACT

A non-aqueous electrolyte battery is disclosed. The non-aqueous electrolyte battery include a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode. The negative electrode includes an anode mixture layer having a volume density of 1.70 to 1.90 g/cm 3  prior to being subjected to charge and discharge processes. The anode mixture layer includes mixed particles composed of spherical graphite having an average particle size of 25 to 35 μm and non-spherical graphite having an average particle size of 8 to 22 μm.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims benefit of priority of Japanese patentApplications No. 2007-296069 filed in the Japanese Patent Office on Nov.14, 2007, and No. 2008-142154 filed in the Japanese Patent Office on May30, 2008, the entire disclosures of which are incorporated herein byreference.

BACKGROUND

The present application relates to a non-aqueous electrolyte battery.More particularly, the present application relates to a non-aqueouselectrolyte battery including a positive electrode and a negativeelectrode which are opposed to each other through a separator.

In recent years, various types of portable electronic devices, such ascamera-integrated videotape recorders (VTRs), cellular phones, andlaptop computers, have come on the market, and those having smaller sizeand weight are being developed. As the portable electronic devices areminiaturized, batteries, particularly secondary batteries as a powersource of them, are vigorously developed.

Among the secondary batteries, a lithium-ion secondary battery whichpossibly achieves high energy density has attracted attention. Withrespect to the lithium-ion secondary battery, by using a laminate filmor the like as a casing member instead of a battery can made of a metal,such as aluminum or iron, the battery is being further reduced in size,weight, and thickness. The lithium-ion secondary battery is used in awide variety of applications, so that a higher energy density in thebattery has been demanded.

For achieving a lithium-ion secondary battery having a higher energy, anattempt is made to increase the volume density of the electrode mixture.For example, Japanese Unexamined Patent Application Publication No.2003-323895 discloses a technique in which different sphericalcarbonaceous materials are used in the electrode mixture to improve theenergy density.

SUMMARY

However, the lithium-ion secondary battery which has a electrode mixturehaving a high volume density suffers marked deformation when theelectrode expands and shrinks repeatedly during the charge and dischargeoperations. Consequently, when the laminate film is used as a casingmember for the lithium-ion secondary battery, the rigidity of thelaminate film is poor as compared to a casing made of a metal, wherebyit is difficult to prevent the battery from suffering deformation due toa change of the pressure in the battery.

Once the electrode deforms, a gap between the electrode and theseparator widens, thereby increasing the cell thickness. Further, whenthe electrode deforms, a gap between the electrode and the separatorwidens, so that the battery capacity considerably deteriorates with anincrease in the number of repetition of charge and discharge cycles.

Accordingly, it is desirable to provide a non-aqueous electrolytebattery which is advantageous in that the electrode mixture layer has ahigh volume density and the battery can be prevented from sufferingdeformation even when using a laminate film as a casing member, thusachieving excellent battery properties.

In accordance with an embodiment, there is provided a non-aqueouselectrolyte battery which includes a positive electrode, a negativeelectrode, and a separator disposed between the positive electrode andthe negative electrode. The negative electrode includes an anode mixturelayer having a volume density of 1.70 to 1.90 g/cm³ prior to beingsubjected to charge and discharge processes. The anode mixture layerincludes mixed particle composed of spherical graphite having an averageparticle size of 25 to 35 μm and non-spherical graphite having anaverage particle size of 8 to 22 μm, thus achieving excellent batteryproperties.

According to an embodiment, the negative electrode has an anode mixturelayer having a volume density of 1.70 to 1.90 g/cm³ prior to beingsubjected to charge and discharge processes, whereby the negativeelectrode having such a high volume density contains mixed particles ofspherical graphite having an average particle size of 25 to 35 μm andnon-spherical graphite having an average particle size of 8 to 22 μm,thus achieving excellent battery properties.

Additional features and advantages are described herein, and will beapparent from the following Detailed Description and the figures.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is an exploded perspective view showing the construction of anon-aqueous electrolyte battery according to an embodiment of thepresent application.

FIG. 2 is a cross-sectional view of the spirally-wound electrodestructure shown in FIG. 1, taken along the line II-II.

DETAILED DESCRIPTION

Hereinbelow, embodiments of the present application will be describedwith reference to accompanying drawings. An example of the constructionof a non-aqueous electrolyte battery according to an embodiment of thepresent application is first described with reference to FIGS. 1 and 2.

FIG. 1 is a perspective view showing an example of the construction of anon-aqueous electrolyte battery according to an embodiment of thepresent application. This non-aqueous electrolyte battery is, forexample, a non-aqueous electrolyte secondary battery. This non-aqueouselectrolyte battery includes a spirally-wound electrode structure 10having fitted thereto a positive electrode lead 11 and a negativeelectrode lead 12 and being contained in a casing member 1 in a filmform, and the battery has a flattened shape.

The positive electrode lead 11 and negative electrode lead 12individually have, for example, a strip shape, and are electricallyextended from the inside of the casing member 1 to the outside, forexample, in the same direction. The positive electrode lead 11 iscomposed of, e.g., a metal material, such as aluminum (Al), and thenegative electrode lead 12 is composed of, e.g., a metal material, suchas nickel (Ni).

The casing member 1 is a laminate film having a structure including, forexample, an insulating layer, a metal layer, and the outermost layerwhich are stacked in this order and bonded together by lamination or thelike. The casing member 1 is disposed so that, for example, theinsulating layer constitutes the inner side, and has the respectiveouter edge portions sealed by heat sealing or by using an adhesive.

The insulating layer is composed of a polyolefin resin, such aspolyethylene, polypropylene, modified polyethylene, modifiedpolypropylene, or a copolymer thereof. The use of these materialsprovides the reduction in moisture permeability of the casing member,thereby achieving excellent airtightness. The metal layer is made ofaluminum, stainless steel, nickel, iron, or the like in the form of foilor plate. The outermost layer may be composed of, for example, the sameresin as that used for the insulating layer, or nylon or the like. Inthis case, the casing member can be improved in resistance to breakage,nail penetration, or the like. The casing member 1 may have any layerother than the insulating layer, metal layer, and outermost layer.

A bonding film 2 is inserted to portions between the casing member 1 andthe positive electrode lead 11, and between the casing member 1 and thenegative electrode lead 12. The bonding film 2 improves the adhesion ofthe positive electrode lead 11 and negative electrode lead 12 to theinner side of the casing member 1 to prevent external air from goinginto the battery. The bonding film 2 is composed of a material havingbonding properties with the positive electrode lead 11 and negativeelectrode lead 12, and, for example, when the positive electrode lead 11and negative electrode lead 12 are individually composed of theabove-mentioned metal material, it is preferred that the bonding film 2is made of a polyolefin resin, such as polyethylene, polypropylene,modified polyethylene, or modified polypropylene.

FIG. 2 is a cross-sectional view of the spirally-wound electrodestructure 10 shown in FIG. 1, taken along the line II-II. Thespirally-wound electrode structure 10 includes a positive electrode 13,a negative electrode 14, a separator 15, and polymer compound layers 16formed on both sides of the separator 15, wherein the separator 15 andpolymer compound layers 16 are disposed between the positive electrode13 and the negative electrode 14. The outermost winding layer ispreferably protected by a protective tape 17, but there can be used noprotective tape.

The positive electrode 13 includes, for example, a positive electrodecurrent collector 13A and cathode mixture layers 13B formed on bothsides of the positive electrode current collector 13A. The positiveelectrode current collector 13A is composed of, for example, a metallicfoil, such as an aluminum foil.

The cathode mixture layer 13B includes, for example, as a cathode activematerial, at least one positive electrode material capable of occludingand releasing lithium (Li) which is an electrode reactive substance, andoptionally a conductor, such as a carbon material, and a binder, such aspolyvinylidene fluoride.

With respect to the positive electrode (cathode) material capable ofoccluding and releasing lithium, a lithium composite oxide havinglithium and a transition metal, a lithium metal phosphate compoundhaving an olivine structure, or the like can be used. Specifically, forexample, LiCoO₂, LiNiO₂, LiMn₂O₄, LiCo_(0.33)Ni_(0.33)Mn_(0.33)O₂, orLiFePO₄ can be used.

As with the positive electrode 13, the negative electrode 14 includes,for example, a negative electrode current collector 14A and anodemixture layers 14B formed on both sides of the negative electrodecurrent collector 14A. The negative electrode current collector 14A iscomposed of, for example, a metallic foil, such as a copper foil.

The anode mixture layer 14B includes, for example, at least one negativeelectrode (anode) material capable of occluding and releasing lithium,and optionally a conductor and a binder.

With respect to the negative electrode (anode) material, a mixture ofspherical graphite and non-spherical graphite is used. The term“spherical graphite” used herein means a carbon material, such asartificial graphite, natural graphite, easily graphitizable carbon, orhardly graphitizable carbon, which has a shape of sphere or substantialsphere. The term “non-spherical graphite” used herein means a carbonmaterial, such as artificial graphite, natural graphite, easilygraphitizable carbon, or hardly graphitizable carbon, which has a shapeof flake, fiber, or bulk. More specifically, examples of sphericalgraphite include mesocarbon microbeads (MCMB) which are artificialgraphite, and examples of non-spherical graphite include powder obtainedby pulverizing MCMB.

The negative electrode material includes mixed particles of sphericalgraphite having an average particle size of 25 to 35 μm andnon-spherical graphite having an average particle size of 8 to 22 μm,and the mixed particles preferably have particle size distribution suchthat D10 is 5 to 11 μm, D50 is 13 to 25 μm, and D90 is 27 to 45 μm. Whenusing the above negative electrode material, excellent properties can beobtained.

In the measurement of particle size distribution, a laserdiffraction-type particle size distribution measuring machine(manufactured and sold by SEISHIN ENTERPRISE CO., LTD.; trade name:LMS-30) or the like can be used. A particle size distribution isrepresented by a particle size distribution in terms of a volume. Forexample, D10 of 5 to 11 μm indicates that a particle size such that thecumulative value of particle size distribution is 10% is 5 to 11 μm. Anaverage particle size is a value of D50 obtained when particle sizedistribution is measured similarly using a laser diffraction-typeparticle size distribution measuring machine (manufactured and sold bySEISHIN ENTERPRISE CO., LTD.; trade name: LMS-30) or the like.

With respect to the mixed particles, there are preferably used mixedparticles of MCMB as spherical graphite and an MCMB pulverized productas non-spherical graphite, which is obtained by pulverizing MCMB andnon-crystallizing the pulverized plane of MCMB. Measurement of X-raydiffraction (XRD) (manufactured and sold by Rigaku Corporation; tradename: RINT) with respect to the mixed particles identifies that themixed particles are composed solely of MCMB. Examination under ascanning electron microscope (SEM) (manufactured and sold by JEOL LTD.;trade name: JSM-5600LV) ascertains that the mixed particles includespherical particles and pulverized particles.

With respect to the negative electrode 14, a negative electrode havingan anode mixture layer 14B having a volume density controlled to fallwithin the range of from 1.70 to 1.90 g/cm³ prior to being subjected tocharge and discharge processes, i.e., a so-called high volume-densitynegative electrode is used. In cell ready for shipping, the anodemixture layer 14B in the completely discharged state preferably has avolume density in the range of from 1.50 to 1.90 g/cm³. The completelydischarged state means a state in which the battery has been dischargedat a constant-current of 0.2 C until the voltage becomes 3.0 V. Cellsready for shipping include, for example, a cell which has been oncecharged to a predetermined voltage, a cell which has been charged onceand discharged to a voltage suitable for shipping, and a cell which hasnot yet been charged and discharged and which is put on the market as aproduct.

The separator 15 is composed of, for example, a porous film made of apolyolefin resin material, such as polypropylene or polyethylene, or aporous film made of an inorganic material, such as ceramic nonwovenfabric, and a separator composed of two or more porous films stackedinto a laminated structure may be used.

The polymer compound layer 16 has a uniform thickness, and includes anelectrolytic solution and a polymer compound retaining the electrolyticsolution, and it is in a so-called gel form. The electrolytic solutionincludes an electrolyte salt and a solvent dissolving the electrolytesalt. Examples of electrolyte salts include lithium salts, such asLiPF₆, LiClO₄, LiBF₄, LiN(CF₃SO₂)₂, LiN(C₂F₅SO₂)₂, and LiAsF₆. Theelectrolyte salts may be used individually or in combination.

Examples of solvents include non-aqueous solvents, e.g., carbonic estersolvents, such as ethylene carbonate, propylene carbonate, vinylenecarbonate, dimethyl carbonate, ethylmethyl carbonate, and diethylcarbonate; ether solvents, such as 1,2-dimethoxyethane,1-ethoxy-2-methoxyethane, 1,2-diethoxyethane, tetrahydrofuran, and2-methyltetrahydrofuran; lactone solvents, such as γ-butyrolactone,γ-valerolactone, δ-valerolactone, and ε-caprolactone; nitrile solvents,such as acetonitrile; sulfolane solvents; phosphoric acid; phosphatesolvents; and pyrrolidone. The solvents may be used individually or incombination.

For improving the properties, an additive, e.g., a cyclic carbonic esterderivative, such as 4-fluoro-1,3-dioxolan-2-one or4,5-difluoro-1,3-dioxolan-2-one, may be added to the solvent.

With respect to the polymer compound, a fluorine polymer compound isused. An example of the fluorine polymer compound include a polymercompound including repeating units derived from vinylidene fluoride.Specific examples include polyvinylidene fluoride and a copolymer ofvinylidene fluoride and hexafluoropropylene. Other fluorine polymercompounds may be used. More specifically, for example,polytetrafluoroethylene and derivatives thereof can be used individuallyor in combination. Polychlorotrifluoroethylene (PCTFE), polyvinylfluoride (PVF), a perfluoroalkoxy fluororesin (PFA), atetrafluoroethylene-hexafluoropropylene copolymer (FEP), anethylene-tetrafluoroethylene copolymer (ETFE), anethylene-chlorotrifluoroethylene copolymer (ECTFE), and the like may beused individually or in combination.

A polymer compound having bonding force other than the fluorine polymercompound may be used. Specifically, for example, polyacrylonitrile,polyethylene oxide, polymethyl methacrylate, polyvinyl chloride, astyrene-butadiene rubber, and derivatives thereof may be usedindividually or in combination.

The polymer compound layer 16 is formed by, for example, forming aporous fluorine polymer compound on the separator 15 and then allowingthe porous fluorine polymer to retain an electrolytic solution. Theporous fluorine polymer compound may be formed by applying a solutionobtained by dissolving a fluorine polymer compound in a solvent, such asN-methyl-2-pyrrolidone (NMP), to both sides of the separator 15 anddrying the solution applied.

It is preferred that the polymer compound layer 16 has a peel strengthof 5 mN/mm or more with the electrode and the separator. A peel strengthcan be measured by, for example, pulling at a rate of 100 mm/min thenegative electrode and separator bonded with each other so that theseparator peels off the negative electrode and determining this peelstrength by means of a digital force gauge (manufactured and sold byIMADA CO., LTD.).

Also when the polymer compound layer 16 contains as filler a compoundhaving a high heat resistance, such as Al₂O₃, SiO₂, TiO₂, or BN (boronnitride), the polymer compound layer maintains its bonding propertiesand hence achieves the similar effect.

Next, an example of the method for producing a non-aqueous electrolytebattery according to an embodiment of the present application isdescribed.

A cathode mixture layer 13B is formed on a positive electrode currentcollector 13A to prepare a positive electrode 13. The cathode mixturelayer 13B is formed by, for example, mixing together a cathode activematerial, a conductor, and a binder and dispersing the resultant mixturein a solvent, such as N-methyl-2-pyrrolidone (NMP), to form a paste, andthen applying the paste to the positive electrode current collector 13Aand drying the paste and subjecting it to compression molding.

An anode mixture layer 14B is formed on a negative electrode currentcollector 14A to prepare a negative electrode 14. The anode mixturelayer 14B is formed by, for example, mixing together an anode activematerial and a binder and dispersing the resultant mixture in a solvent,such as N-methyl-2-pyrrolidone (NMP), to form a paste, and then applyingthe paste to the negative electrode current collector 14A and drying thepaste and subjecting it to compression molding. Then, a positiveelectrode lead 11 is fitted to the positive electrode current collector13A, and a negative electrode lead 12 is fitted to the negativeelectrode current collector 14A.

A solution obtained by dissolving a fluorine polymer compound in asolvent, such as N-methyl-2-pyrrolidone (NMP), is applied to both sidesof a separator 15, and the resultant separator is immersed into a poorsolvent, such as water, and then dried using hot air or the like to forma porous fluorine polymer compound layer on both sides of the separator15.

The positive electrode 13, separator 15, negative electrode 14, andseparator 15 are stacked on one another and spirally wound together, anda protective tape 17 is bonded with the outermost winding layer to forma spirally-wound electrode structure 10, and then the electrodestructure is disposed between a folded casing member 1, and three sidesof the outer edge portion of the casing member 1 are heat-sealed under areduced pressure. In this instance, a bonding film 2 is inserted intoportions between the positive electrode lead 11 and the casing member 1and between the negative electrode lead 12 and the casing member 1.

Then, an electrolytic solution is injected into the resultant casingmember, and the remaining one side of the outer edge portion isheat-sealed under a reduced pressure to hermetically seal the casingmember. The casing member is finally hot-pressed to obtain a non-aqueouselectrolyte battery according to an embodiment. Upon heating for the hotpressing, part of or whole of the porous fluorine polymer compoundbecomes in a gel form, thus forming a polymer compound layer 16.

EXAMPLES

The present application will be described in more detail with referenceto the following Examples, which should not be construed as limiting thescope of the present application.

Studies on optimum negative electrode

Sample 1

As a negative electrode material, mixed particles including sphericalgraphite having an average particle size of 31.7 μm and non-sphericalgraphite having an average particle size of 7.2 μm mixed in a 1:1 massratio, and having particle size distribution such that D10 is 4.1 μm,D50 is 10.5 μm, D90 is 29.6 μm were prepared. To the mixed particles wasadded PVdF as a binder, and the resultant mixture was dispersed in NMPas a solvent, and the dispersion was applied to a Cu foil and dried,followed by pressing so that the volume density of the anode mixturelayer became 1.85 g/cm³. When the volume density did not become 1.85g/cm³, pressing was controlled so that the volume density was close tothat value. Pressing was conducted to achieve a volume density of 1.82g/cm³, thus preparing a negative electrode of sample 1.

Sample 2

A negative electrode of sample 2 was prepared in the same manner as insample 1, except that, as a negative electrode material, mixed particlesincluding spherical graphite having an average particle size of 31.7 μmand non-spherical graphite having an average particle size of 11.7 μmmixed in a 1:1 mass ratio, and having particle size distribution suchthat D10 is 5.5 μm, D50 is 15.2 μm, and D90 is 31.4 μm were prepared,and that the anode mixture layer had a volume density of 1.85 g/cm³.

Sample 3

A negative electrode of sample 3 was prepared in the same manner as insample 1, except that, as a negative electrode material, mixed particlesincluding spherical graphite having an average particle size of 31.7 μmand non-spherical graphite having an average particle size of 14.1 μmmixed in a 1:1 mass ratio, and having particle size distribution suchthat D10 is 8.5 μm, D50 is 21.9 μm, and D90 is 37.8 μm were prepared,and that the anode mixture layer had a volume density of 1.85 g/cm³.

Sample 4

A negative electrode of sample 4 was prepared in the same manner as insample 1, except that, as a negative electrode material, mixed particlesincluding spherical graphite having an average particle size of 31.7 μmand non-spherical graphite having an average particle size of 20.3 μmmixed in a 1:1 mass ratio, and having particle size distribution suchthat D10 is 9.7 μm, D50 is 23.6 μm, and D90 is 41.5 μm were prepared,and that the anode mixture layer had a volume density of 1.85 g/cm³.

Sample 5

A negative electrode of sample 5 was prepared in the same manner as insample 1, except that, as a negative electrode material, mixed particlesincluding spherical graphite having an average particle size of 42.1 μmand non-spherical graphite having an average particle size of 7.2 μmmixed in a 1:1 mass ratio, and having particle size distribution suchthat D10 is 4.1 μm, D50 is 11.6 μm, and D90 is 48.6 μm were prepared,and that the anode mixture layer had a volume density of 1.79 g/cm³.

Sample 6

A negative electrode of sample 6 was prepared in the same manner as insample 1, except that, as a negative electrode material, mixed particlesincluding spherical graphite having an average particle size of 42.1 μmand non-spherical graphite having an average particle size of 11.7 μmmixed in a 1:1 mass ratio, and having particle size distribution suchthat D10 is 5.7 μm, D50 is 14.8 μm, and D90 is 48.7 μm were prepared.

Sample 7

A negative electrode of sample 7 was prepared in the same manner as insample 1, except that, as a negative electrode material, mixed particlesincluding spherical graphite having an average particle size of 42.1 μmand non-spherical graphite having an average particle size of 14.1 μmmixed in a 1:1 mass ratio, and having particle size distribution suchthat D10 is 7.4 μm, D50 is 21.7 μm, and D90 is 48.8 μm were prepared,and that the anode mixture layer had a volume density of 1.82 g/cm³.

Sample 8

A negative electrode of sample 8 was prepared in the same manner as insample 1, except that, as a negative electrode material, mixed particlesincluding spherical graphite having an average particle size of 42.1 μmand non-spherical graphite having an average particle size of 20.3 μmmixed in a 1:1 mass ratio, and having particle size distribution suchthat D10 is 9.8 μm, D50 is 24.7 μm, and D90 is 49.2 μm were prepared,and that the anode mixture layer had a volume density of 1.80 g/cm³.

Sample 9

A negative electrode of sample 9 was prepared in the same manner as insample 1, except that, as a negative electrode material, mixed particlesincluding spherical graphite having an average particle size of 51.3 μmand non-spherical graphite having an average particle size of 11.7 μmmixed in a 1:1 mass ratio, and having particle size distribution suchthat D10 is 5.7 μm, D50 is 15.7 μm, and D90 is 57.7 μm were prepared,and that the anode mixture layer had a volume density of 1.75 g/cm³.

Sample 10

A negative electrode of sample 10 was prepared in the same manner as insample 1, except that, as a negative electrode material, mixed particlesincluding spherical graphite having an average particle size of 51.3 μmand non-spherical graphite having an average particle size of 14.1 μmmixed in a 1:1 mass ratio, and having particle size distribution suchthat D10 is 7.5 μm, D50 is 23.3 μm, and D90 is 57.8 μm were prepared,and that the anode mixture layer had a volume density of 1.73 g/cm³.

Evaluation of Capacity

Coin cells were individually prepared using the negative electrodes ofsamples 1 to 10, and a capacity of each coin cell was measured.

With respect to the positive electrode, there was used a positiveelectrode obtained by mixing together lithium cobaltate, ketjen black,and polyvinylidene fluoride (PVdF) in a 7:2:1 ratio, and dispersing theresultant mixture in N-methyl-2-pyrrolidone (NMP) and applying thedispersion to an Al foil and then drying the dispersion applied. Thecoating weight was adjusted to 1.5 times the coating weight in thenegative electrode.

The positive electrode and negative electrode were individually punchedinto discs, and the resultant positive electrode and negative electrodeand a separator composed of a microporous polyethylene film were stackedon one another in the order of the positive electrode, separator, andnegative electrode, and the resultant stacked structure was placed in abattery can.

Then, an electrolytic solution, which was obtained by dissolving LiPF₆in a mixed solvent including ethylene carbonate and diethyl carbonate ina 3:7 mass ratio so that the concentration became 1.0 mol/l, wasinjected into the battery can, followed by caulking of the battery canthrough an insulating gasket, thereby obtaining a coin cell.

With respect to the coin cell obtained, a constant-current andconstant-voltage charging at a charge current of 1 C was conducted at anupper limit voltage of 4.2 V for 2 hours, and then a 0.2 Cconstant-current discharging was conducted until the voltage became acut-off voltage of 3.0 V, and a discharge capacity was measured, and thecapacity was evaluated using a value determined from the followingformula.

Formula:

(Initial discharge capacity)/(Theoretical capacity)×100(%)

The results of measurement are shown in Table 1.

TABLE 1 Particle size distribution (Initial discharge SphericalNon-spherical of mixed Volume capacity)/(Theoretical Negative graphitegraphite particles (μm) density capacity) electrode (μm) (μm) D10 D50D90 (g/cm³) (%) Sample 1 31.7 7.2 4.1 10.5 29.6 1.82 92 Sample 2 31.711.7 5.5 15.2 31.4 1.85 92 Sample 3 31.7 14.1 8.5 21.9 37.8 1.85 93Sample 4 31.7 20.3 9.7 23.6 41.5 1.85 92 Sample 5 42.1 7.2 4.1 11.6 48.61.79 88 Sample 6 42.1 11.7 5.7 14.8 48.7 1.85 88 Sample 7 42.1 14.1 7.421.7 48.8 1.82 87 Sample 8 42.1 20.3 9.8 24.7 49.2 1.80 87 Sample 9 51.311.7 5.7 15.7 57.7 1.75 84 Sample 10 51.3 14.1 7.5 23.3 57.8 1.73 84

As can be seen from Table 1, samples 2 to 4 achieve excellentproperties.

Studies on Effect of Polymer Compound Layer

Using the negative electrode of sample 3, a laminate cell (A) and alaminate cell (B) were individually prepared as follows.

Laminate cell (A)

With respect to the positive electrode, there was used a positiveelectrode obtained by mixing together lithium cobaltate, ketjen black,and PVdF in a 7:2:1 (mass ratio), and dispersing the resultant mixturein NMP and applying the dispersion to both sides of an Al foil and thendrying the dispersion applied. The coating amount was adjusted to 1.5times the coating amount in the negative electrode.

With respect to the negative electrode, as with the negative electrodeof sample 3, there was used a negative electrode obtained by adding PVdFas a binder to the mixed particles prepared in the same manner as insample 3, and dispersing the resultant mixture in NMP as a solvent andapplying the dispersion to both sides of a Cu foil and drying thedispersion applied, and then pressing the resultant foil so that thevolume density of the anode mixture layer became 1.85 g/cm³.

With respect to the separator, a microporous polyethylene film was used.A solution obtained by dissolving PVdF in NMP so that the concentrationbecame 15 wt % was applied to both sides of the separator and dried toform porous polyvinylidene fluoride having a thickness of 5 μm on theboth sides of the separator.

A terminal was attached to each of the positive electrode and negativeelectrode prepared as described above, and then the positive electrodeand negative electrode were put together through the separator coatedwith a porous fluororesin, and they were spirally wound together in thelongitudinal direction to prepare a battery element.

The prepared battery element was sandwiched with a casing membercomposed of a laminate film, and three sides of the casing member wereheat-sealed. With respect to the casing member, there was used amoisture-proof aluminum laminate film including a nylon film having athickness of b 25 μm, an aluminum foil having a thickness of 40 μm, anda polypropylene film having a thickness of 30 μm, which were stacked onone another in this order from the outermost layer.

Then, an electrolytic solution was injected into the resultant casingmember containing the battery element, and the remaining one side washeat-sealed under a reduced pressure to hermetically seal the casingmember. With respect to the electrolytic solution, there was used anelectrolytic solution obtained by dissolving LiPF₆ in a mixed solventcomprising ethylene carbonate and diethyl carbonate in a 3:7 mass ratioso that the concentration became 1 mol/l. The casing member containingthe battery element was sandwiched between iron plates and heated at 70°C. for 3 minutes to bond together the positive electrode, negativeelectrode, and separator through the porous polyvinylidene fluoride,thereby preparing a laminate cell (A).

Laminate Cell (B)

A laminate cell (B) was prepared in the same manner as in the laminatecell (A), except that no porous polyvinylidene fluoride was formed onboth sides of the separator.

With respect to each of the laminate cells (A) and (B), a charging anddischarging test was conducted, and a capacity retention ratio and athickness increase ratio were measured.

Measurement of Capacity Retention Ratio

A capacity retention ratio was measured by a method in which one cycleof charge and discharge operation was conducted and then 300 cycles ofcharge and discharge operations were conducted, and a discharge capacityin the 1st cycle and a discharge capacity in the 300th cycle weremeasured and a capacity retention ratio was determined from thefollowing formula.

Formula:

Capacity retention ratio (%)=(Discharge capacity in 300thcycle)/(Discharge capacity in 1st cycle)×100(%)

With respect to the charging, a constant-current and constant-voltagecharging at a charge current of 1.0 C was conducted at an upper limitvoltage of 4.2 V for 2 hours. With respect to the discharging, a 1.0 Cconstant-current discharging was conducted until the voltage became acut-off voltage of 3.0 V

Measurement of Thickness Increase Ratio

Under the same conditions as those in the measurement of capacityretention ratio, 300 cycles of charge and discharge operations wereconducted, and subsequently a thickness of the battery in the chargedstate in the 1st cycle and a thickness of the battery in the chargedstate in the 300th cycle were measured, and a thickness increase ratiowas determined from the following formula.

Formula:

Thickness increase ratio (%)=((Thickness after discharging in 300thcycle)−(Thickness after discharging in 1st cycle))/(Thickness afterdischarging in 1st cycle)×100(%)

A thickness of the battery was measured by means of Digimatic Indicator(manufactured and sold by Mitutoyo Corporation) in a state such that thebattery was sandwiched between two parallel plates so that a differencein thickness was not caused between the measurement sites.

The results of measurements are shown in Table 2.

TABLE 2 Capacity Thickness increase Polyvinylidene retention ratio ratiofluoride (%) (%) Laminate cell (A) Formed 83 3 Laminate cell (B) Notformed 58 11

As can be seen from Table 2, the laminate cell (A), in which porouspolyvinylidene fluoride was formed on both sides of the separator,achieved more excellent capacity retention ratio and thickness increaseratio than those of the laminate cell (B). The similar results areprobably obtained with respect to the laminate cells prepared using thenegative electrodes of samples 2 and 4.

Studies on effect according to composition of electrolytic solution andthe like

Experiments were made to check whether a similar effect was obtainedwhen the composition of the electrolytic solution was changed or anadditive was further added. Laminate cells (C) to (K) shown below arethe same as the laminate cell (A), except that the composition of theelectrolytic solution is changed or an additive is further added, and,in these laminate cells, a bonding layer composed of polyvinylidenefluoride (PVdF) is formed between the electrode and the separator.

Laminate Cell (C)

A laminate cell (C) was prepared in the same manner as in the laminatecell (A) except that an electrolytic solution obtained by dissolvingLiPF₆ in a mixed solvent including ethylene carbonate (EC) andethylmethyl carbonate (EMC) in a 30:70 mass ratio so that theconcentration became 1 mol/l was used.

Laminate Cell (D)

A laminate cell (D) was prepared in the same manner as in the laminatecell (A), except that an electrolytic solution obtained by dissolvingLiPF₆ in a mixed solvent including ethylene carbonate (EC) and dimethylcarbonate (DMC) in a 30:70 mass ratio so that the concentration became 1mol/l was used.

Laminate Cell (E)

A laminate cell (E) was prepared in the same manner as in the laminatecell (A), except that an electrolytic solution obtained by dissolvingLiPF₆ in a mixed solvent including ethylene carbonate (EC), diethylcarbonate (DEC), and propylene carbonate (PC) in a 25:70:5 mass ratio sothat the concentration became 1 mol/l was used.

Laminate Cell (F)

A laminate cell (F) was prepared in the same manner as in the laminatecell (A), except that an electrolytic solution obtained by dissolvingLiPF₆ in a mixed solvent including ethylene carbonate (EC), ethylmethylcarbonate (EMC), and propylene carbonate (PC) in a 25:70:5 mass ratio sothat the concentration became 1 mol/l was used.

Laminate Cell (G)

A laminate cell (G) was prepared in the same manner as in the laminatecell (A), except that an electrolytic solution obtained by adding4-fluoro-1,3-dioxolan-2-one (FEC) in an amount of 1.0 wt % to a mixedsolvent including ethylene carbonate (EC) and diethyl carbonate (DEC) ina 30:70 mass ratio and dissolving LiPF₆ in the resultant solvent so thatthe concentration became 1 mol/l was used.

Laminate Cell (H)

A laminate cell (H) was prepared in the same manner as in the laminatecell (A), except that an electrolytic solution obtained by adding4-fluoro-1,3-dioxolan-2-one (FEC) in an amount of 1.0 wt % to a mixedsolvent including ethylene carbonate (EC), diethyl carbonate (DEC), andpropylene carbonate (PC) in a 25:70:5 mass ratio and dissolving LiPF₆ inthe resultant solvent so that the concentration became 1 mol/l was used.

Laminate Cell (I)

A laminate cell (I) was prepared in the same manner as in the laminatecell (A), except that an electrolytic solution obtained by adding4-fluoro-1,3-dioxolan-2-one (FEC) in an amount of 1.0 wt % to a mixedsolvent including ethylene carbonate (EC), ethylmethyl carbonate (EMC),and propylene carbonate (PC) in a 25:70:5 mass ratio and dissolvingLiPF₆ in the resultant solvent so that the concentration became 1 mol/lwas used.

Laminate Cell (J)

A laminate cell (J) was prepared in the same manner as in the laminatecell (A), except that an electrolytic solution obtained by dissolvingLiPF₆ in a mixed solvent including ethylene carbonate (EC), diethylcarbonate (DEC), and ethylmethyl carbonate (EMC) in a 30:35:35 massratio so that the concentration became 1 mol/l was used.

Laminate Cell (K)

A laminate cell (K) was prepared in the same manner as in the laminatecell (A), except that an electrolytic solution obtained by adding4-fluoro-1,3-dioxolan-2-one (FEC) in an amount of 1.0 wt % to a mixedsolvent including ethylene carbonate (EC), diethyl carbonate (DEC), andethylmethyl carbonate (EMC) in a 30:35:35 mass ratio and dissolvingLiPF₆ in the resultant solvent so that the concentration became 1 mol/lwas used.

With respect to each of the laminate cells (C) to (K) prepared, acapacity retention ratio and a thickness increase ratio after the 300cycles were measured in the same manner as in the laminate cell (A).

The results of measurements for the laminate cells (C) to (K) andlaminate cell (A) are shown in Table 3.

TABLE 3 Capacity Thickness Formulation of electrolytic FEC retentionincrease solution (Mass ratio) (wt ratio ratio EC DEC EMC DMC PC %) (%)(%) Laminate 30 70 0 0 0 0 83 3.0 cell (A) Laminate 30 0 70 0 0 0 80 4.2cell (C) Laminate 30 0 0 70 0 0 79 4.6 cell (D) Laminate 25 70 0 0 5 081 4.1 cell (E) Laminate 25 0 70 0 5 0 78 4.9 cell (F) Laminate 30 70 00 0 1 86 2.2 cell (G) Laminate 25 70 0 0 5 1 83 3.2 cell (H) Laminate 250 70 0 5 1 82 3.8 cell (I) Laminate 30 35 35 0 0 0 81 4.0 cell (J)Laminate 30 35 35 0 0 1 83 3.3 cell (K) EC: Ethylene carbonate DEC:Diethyl carbonate EMC: Ethylmethyl carbonate DMC: Dimethyl carbonate PC:Propylene carbonate FEC: 4-Fluoro-1,3-dioxolan-2-one

As can be seen from Table 3, the laminate cells having variousformulations of electrolytic solution achieved excellent results. Inaddition, the above results have ascertained that the use of anadditive, such as 4-fluoro-1,3-dioxolan-2-one (FEC), possibly furtherimproves the properties. The reason that expansion was suppressed when4-fluoro-1,3-dioxolan-2-one (FEC) was added resides in that a film isformed on the surface of the negative electrode during the initialcharging to suppress decomposition of the electrolytic solution (gasgeneration) on the surface of the charged negative electrode. When thethickness increase ratio is 9% or less, a capacity retention ratio of70% or more can be expected.

Change of negative electrode volume density due to charge and dischargeoperations

Test Example

With respect to the negative electrode, as with the negative electrodeof sample 3, there was used a negative electrode obtained by adding PVdFas a binder to the mixed particles prepared in the same manner as insample 3, and dispersing the resultant mixture in NMP as a solvent andapplying the dispersion to both sides of a Cu foil and drying thedispersion applied, and then pressing the resultant foil so that thevolume density of the anode mixture layer became 1.80 g/cm³. Using thisnegative electrode, a laminate cell was prepared in the same manner asin the laminate cell (A).

With respect to the laminate cell prepared, one cycle of charge anddischarge operation at an upper limit voltage of 4.2 V, 4.3 V, or 4.4 Vwas conducted, and a volume density of the anode mixture layer in thecompletely discharged state was measured. With respect to the charging,a constant-current and constant-voltage charging at a charge current of1.0 C was conducted at a charge voltage of 4.2 V, 4.3 V, or 4.4 V for 2hours. With respect to the discharging, a 0.2 C constant-currentdischarging was conducted until the voltage became a cut-off voltage of3.0 V.

The results of measurement are shown in Table 4.

TABLE 4 Volume density of anode mixture layer Volume density of anode ofelectrode Charge mixture layer in completely just prepared voltagedischarged state (g/cm³) (V) (g/cm³) Test example 1.80 4.2 1.64 4.3 1.614.4 1.59

As can be seen from Table 4, as the charge voltage increases and theelectrode more markedly expands, the electrode hardly shrinks in thecomplete discharge until the voltage becomes 3 V, so that the volumedensity tends to be smaller.

According to embodiments, the volume density of the electrode mixturelayer is high, and the battery can be prevented from sufferingdeformation even when using a laminate film as a casing member, thusachieving excellent battery properties. Further, in the presentapplication, the volume density of the electrode mixture layer can beincreased, making it possible to produce a battery having high energydensity.

The present application is not limited to the above embodiment of thepresent application, and can be changed or modified as long as thenon-aqueous electrolyte battery of the present application can beobtained. For example, in the non-aqueous electrolyte battery accordingto an embodiment, with respect to the shape of cylinder, rectangle, orthe like, there is no particular limitation, and the battery may be ofvarious sizes, such as a thin type or a large size. Furthermore, thenon-aqueous electrolyte battery is not limited to the secondary battery,and can be applied to other batteries, such as a primary battery.

It should be understood that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications can be madewithout departing from the spirit and scope of the present subjectmatter and without diminishing its intended advantages. It is thereforeintended that such changes and modifications be covered by the appendedclaims.

1. A non-aqueous electrolyte battery comprising: a positive electrode; anegative electrode; and a separator disposed between the positiveelectrode and the negative electrode, wherein the negative electrodeincludes an anode mixture layer having a volume density of 1.70 to 1.90g/cm³ prior to being subjected to charge and discharge processes, andwherein the anode mixture layer includes mixed particles composed ofspherical graphite having an average particle size of 25 to 35 μm andnon-spherical graphite having an average particle size of 8 to 22 μm. 2.The non-aqueous electrolyte battery according to claim 1, whereinpolymer compound layers are disposed between the negative electrode andthe separator, and between the positive electrode and the separator. 3.The non-aqueous electrolyte battery according to claim 2, wherein thepolymer compound layer is composed of a porous polymer compoundretaining an electrolytic solution therein.
 4. The non-aqueouselectrolyte battery according to claim 3, wherein the polymer compoundlayer has a uniform thickness.
 5. The non-aqueous electrolyte batteryaccording to claim 1, wherein the mixed particles have particle sizedistributions such that D10 is 5 to 11 μm, D50 is 13 to 25 μm, and D90is 27 to 45 μm.
 6. The non-aqueous electrolyte battery according toclaim 1, wherein: the spherical graphite is mesocarbon microbeads; andthe non-spherical graphite is a powder obtained by pulverizingmesocarbon microbeads.
 7. The non-aqueous electrolyte battery accordingto claim 2, wherein the polymer compound layer contains a polymercompound including repeating units derived from vinylidene fluoride. 8.The non-aqueous electrolyte battery according to claim 2, wherein thepolymer compound layer contains a copolymer including at least repeatingunits derived from vinylidene fluoride and repeating units derived fromhexafluoropropylene.
 9. The non-aqueous electrolyte battery according toclaim 2, wherein the polymer compound layer has a bonding strength of 5mN/mm or more with the electrode and the separator.
 10. The non-aqueouselectrolyte battery according to claim 2, wherein: the positiveelectrode, the negative electrode, the separator, and the polymercompound layer are spirally wound together to form a battery element;and the battery has a flattened shape.
 11. The non-aqueous electrolytebattery according to claim 10, further comprising a casing member forcontaining the battery element therein, the casing member being composedof a moisture-proof laminate film including a polymer film and ametallic foil.
 12. The non-aqueous electrolyte battery according toclaim 1, wherein the anode mixture layer has a volume density of 1.50 to1.90 g/cm³ with respect to a cell ready for shipping, the cell beingsubjected to 0.2 C constant-current discharging until becoming a cut-offvoltage of 3.0 V.